Optical fiber assemblies

ABSTRACT

Fiber optic assemblies include subunit cables wrapped in binders. The assemblies have small cross sections and low bend radii while maintaining acceptable attenuation losses. SZ stranding of the subunit cables allows ease of access to the individual cables during installation.

PRIORITY APPLICATION

This is a continuation of PCT/US2009/60163, filed Oct. 9, 2009, whichclaims the benefit of U.S. Prov. App. No. 61/104,142, filed Oct. 9,2008, and 61/245,420, filed Sep. 24, 2009, the entire contents of whichare hereby incorporated by reference.

TECHNICAL FIELD

The present application relates generally optical fiber assemblieshaving low bend radii and small cross-sectional areas.

BACKGROUND

Communications networks are used to transport a variety of signals suchas voice, video, data and the like. As communications applicationsrequired greater bandwidth, communication networks switched to fiberoptic cables since they are capable of transmitting an extremely largeamount of bandwidth compared with copper conductors. Fiber optic cablesare also much smaller and lighter compared with copper cables having thesame bandwidth capacity. Conventional fiber optic cables, however, maybe too large or rigid for some applications. For example, in a multipledwelling unit (MDU) such as an apartment building, it is often necessaryto run fiber optic cables through small spaces and around tight cornersto provide access to individual dwelling units. Conventional fiber opticcables often are either too large in cross-section, too inflexible, orboth, to be run to individual dwelling units.

Conventional MDU deployments also require pulling individual cables fromthe fiber distribution terminal (FDT) to each living unit. Thetechnician typically unspools a cable down a hallway and then placesthem into a raceway molding. The raceway can become congested withcables, however, and the technician may be required to pull from 6-12individual drop cables from the FDT to the living units. The timerequired to pull off of individual reels can also be disruptive to MDUtenants and add to labor costs of installation.

SUMMARY

According to one embodiment, a fiber optic assembly comprises a bundledunit of a plurality of single fiber subunit fiber optic cables strandedtogether. The bundle of subunit fiber optic cables may be wrapped withone or more binders to secure the subunit cables in place. The subunitcables can be SZ stranded to facilitate access to individual subunits.The subunit cables can have flame retardant properties to achievedesired flame ratings for the fiber optic assembly.

According to one aspect of the first embodiment, the stranded bundle ofsubunit fiber optic cables forming the fiber optic assembly does notrequire a conventional central strength member component, such as a GRProd, or an outside cable sheath. Omission of the central strengthcomponent and/or outer jacket in part gives the fiber optic assembly anextremely small bending radius and a small cross-section.

According to another aspect, one or more of the subunit fiber opticcables can have an integral, individual strength component. The strengthcomponent can comprise a layer of flexible, loose tensile strengthmembers. Accordingly, the fiber optic assembly incorporating the subunitcables can have extremely high tensile strength, while not beingexcessively rigid or inflexible such as cables having rigid centralstrength members.

According to yet another aspect, the subunit fiber optic cables caninclude one or more bend-insensitive optical fibers. The fiber opticassembly can therefore be bent around tight corners, etc. withoutexcessive attenuation losses in the individual optical fibers. In use,the subunit fiber optic cables can be separated from the fiber opticalassembly and run to separate locations. The use of bend-insensitiveoptical fibers allows the subunit cables to be run through extremelytight locations and along tortuous paths.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features of the drawings are not necessarily drawn to scale.

FIG. 1 is a perspective view of a portion of a fiber optic assemblyaccording to a first embodiment of the invention.

FIG. 2 is a cross-sectional view of the fiber optic assembly illustratedin FIG. 1 taken on line 2-2 in FIG. 1.

FIG. 3 is a perspective partial cutaway view of a portion of a subunitfiber optic cable used in the fiber optic assembly illustrated in FIG.1.

FIG. 4 is a cross-sectional view of the subunit fiber optic cableillustrated in FIG. 3 taken on line 4-4 in FIG. 3.

FIG. 5 illustrates bend characteristics of the fiber optic assemblyillustrated in FIG. 1.

FIG. 6 is another depiction of bend characteristics of the fiber opticassembly illustrated in FIG. 1.

FIG. 7 is a depiction of characteristic dimensions for the fiber opticassembly illustrated in FIG. 1.

FIG. 8 is a perspective view of a portion of a fiber optic assemblyaccording to a second embodiment of the invention.

FIG. 9 is a cross-sectional view of the fiber optic assembly illustratedin FIG. 8 taken on line 9-9 in FIG. 8.

FIG. 10 is a perspective view of a portion of a fiber optic assemblyaccording to a third embodiment of the invention.

FIG. 11 is a cross-sectional view of the fiber optic assemblyillustrated in FIG. 10 taken on line 11-11 in FIG. 10.

FIG. 12 is a plot of delta attenuation in a mandrel wrap test at 1550nanometers for the cable of FIGS. 10-11.

FIG. 13 is a plot of delta attenuation in a corner bend test at 1550nanometers for the cable of FIGS. 10-11.

DETAILED DESCRIPTION

Reference will now be made in detail to the present embodiments,examples of which are illustrated in the accompanying drawings. Wheneverpossible, the same reference numerals will be used throughout thedrawings to refer to the same or like parts.

FIG. 1 is a perspective view of a portion of a fiber optic assembly 10or bundled optical cable according to a first embodiment of theinvention. FIG. 2 is a cross-sectional view of the fiber optic assembly10 taken on line 2-2 in FIG. 1. Referring to FIGS. 1 and 2, the fiberoptic assembly 10 comprises a bundled unit of a plurality of subunitfiber optic cables 100. The subunit cables 100 are wrapped with one ormore binders to secure the subunit cables 100 in place. In theillustrated embodiment, a pair of oppositely helically wound outer orexternal binders 110, 114 are wound about the external periphery of thebundle of subunit cables 100. One or more inner binders can be helicallywound about an inner layer 120 of the subunit cables 100. In theillustrated embodiment, a single inner binder 118 is wound about thethree inner subunit cables 100 that constitute an inner layer 120 ofsubunit cables. The outer layer 130 of subunit cables 100 is constitutedby the nine subunit cables surrounding the inner layer 120 in a “9-3”arrangement.

In the illustrated embodiment, the subunit cables 100 are SZ strandedtogether. SZ stranding is advantageous in that it facilitates mid-spanaccess of the subunit cables 100, and important feature when the cables100 are to be deployed throughout structures such as multiple dwellingunits. The outer binders 110, 114 may be contra-helically stranded aboutthe outer layer 130 of subunit cables 100, and the inner binder 118 maybe helically wrapped about the inner layer 120. In general, the laylength of the helically wrapped external binders 110, 114 is smallerthan the lay length of the subunit cables 100, but other suitable laylengths are possible. The adjoining inner and outer layers 120, 130 ofsubunit cables 100 can be stranded in separate passes on separatestranders, or on a common strander in a single pass. The subunit cables100 of the inner layer 120 may be immediately adjacent and contactingthose of the outer layer 130, with only the binder 110 being interposedbetween the layers.

The binders 110, 114, 118 stranded about the subunit fiber optic cables100 can be made from high tensile strength materials to enhance thetensile strength of the fiber optic assembly 10. For example, thebinders can be formed from elongate tensile yarns, such as aramid,fiberglass, polyester and other tensile yarns.

FIG. 3 is a perspective partial cutaway view of a portion of a subunitfiber optic cable 100 used in the fiber optic assembly 10 shown inFIG. 1. FIG. 4 is a cross-sectional view of the subunit fiber opticcable 100 taken on line 4-4 in FIG. 3. The subunit fiber optic cables100 can be, for example, flame retardant single fiber cables. In theillustrated embodiment, the subunit fiber optic cable 100 includes asingle optical fiber 150 surrounded by a buffer coating 154 applied overthe optical fiber 150. The optical fiber 150 may contain a core and acladding surrounding the core, with one or more polymer coatings appliedover the cladding. A layer 158 of loose tensile strength memberssurrounds the buffer coating 154, and an outer polymer tubular subunitjacket or sheath 160 is extruded over the layer 158 of strength members.According to the present embodiments, the layer 158 of loose tensilestrength members adds sufficient tensile strength to the individualfiber optic subunits such that additional strength members are notrequired for the overall assembly 10. For example, assemblies asdisclosed herein can be free of rigid strength members such asglass-reinforced plastic (GRP) rods, which add cost and increase thebend radii of cables.

The buffer coating 154 may be formed of a polyvinyl chloride (PVC)material. Other suitable materials for the coating 154 include polymericmaterials such as ultraviolet light cured acrylate materials,polyethylene, PVDF, nylon or PVR. The outer subunit jacket 160 may beformed of PVC material, for example. Other suitable materials for theouter subunit jacket 160 include polymeric materials such aspolyethylene, PVDF, or nylon. The layer 158 of tensile strength memberscan be aramid fiber yarns such as KEVLAR® available from E.I. du Pont deNemours and Co., fiberglass, and aramid-reinforced plastics (ARP). Thesubunit jacket 160 and/or the coating 154 can include aluminumtrihydrate, antimony trioxide, or other suitable additives to improveflame resistance.

The optical fibers 150 used in the subunit fiber optic cables 100 may bebend-insensitive optical fibers. Examples of bend-insensitive opticalfibers include the ClearCurve™ brand of optical fibers available fromCorning Incorporated. Such fibers may have bend radii as low as 5 mmwith low attenuation.

The fiber optic assembly 10 can have a very small bend diameter whilemaintaining acceptable attenuation losses. FIG. 5 illustrates theability of the fiber optic assembly 10 to be essentially folded back onitself without undue effort. The bend insensitive fibers used in thesubunit fiber optic cables 100 can bend at radii of 5 mm, so there is noexcess attenuation in the fiber optic assembly 10 in tight bends. FIG. 6illustrates winding of the fiber optic assembly 10 around asmall-diameter mandrel. The illustrated mandrel has a diameter of about⅛ inch (3.2 mm). With the extremely tight possible bend configurationsof the fiber optic assembly 10, the assembly is essentiallyself-limiting in bend characteristics. In other words, the technicianinstalling the fiber optic assembly 10 will not likely be capable ofbending the fiber optic assembly in such a way as to induce unacceptableattenuation, and the tightness of the bend diameter is insteaddetermined by the structure of the fiber optic assembly. As used herein,the “bend diameter” induced in a cable or fiber optic assembly can beobtained by wrapping the cable or fiber optic assembly about an elongateelement of circular cross-section. The diameter of the elongate elementis the bend diameter.

FIG. 7 illustrates characteristic dimensions for the fiber opticassembly 10. In FIG. 7, the fiber optic assembly 10 is illustrated ashaving an idealized cross-sectional area A which is defined by a circle(shown in dashed lines) that encompasses the fiber optic assembly 10,and a cable diameter CD. The cable diameter CD generally will not beuniform across different parts for the cable cross-section, and may alsovary slightly along the length of the fiber optic assembly 10. Anaverage or mean cable diameter may be measured, for example, by takingseveral width or thickness measurements along the fiber optic assemblyusing a micrometer. The absence of a central strength member (e.g. GRProd) and outer jacket means the fiber optic assembly 10 has a relativelysmall cross-sectional area A and cable diameter CD when compared withsimilar cables having an equivalent fiber count. According to thepresent embodiments, the bundled unit size of the fiber optic assembly10 is substantially smaller than, for example, a comparable 12-fiber fanout cable assembly. For example, the fiber optic assembly 10 havingtwelve subunit fiber optic cables 100 may have a cable diameter CD ofabout 12.5 mm or less. In another embodiment, the cable diameter CD maybe about 11.5 mm or less. By contrast, a comparable conventional riserfan out cable has an average cable diameter of about 13.5 mm. Keepingthe size less than 12.7 mm (½ inch) ensures that the fiber opticassembly 10 can be routed through a short section of ½ inch conduit.

The fiber optic assembly 10 can be adapted for indoor use, for example,such that an outside cable sheath for the fiber optic assembly isunnecessary. The absence of an outer jacket, as well as omitting acentral strength member, in part provides the fiber optic assembly 10with its relatively low bend diameter. By contrast, in conventionalcables, maximum allowable strains on the outer surface of the cablejacket limit the cable bending radius to at least about 5 to 10 timesthe outer cable diameter. Each subunit cable 100 may be provided with aflexible strength component, such as the layer 158, so that the fiberoptic assembly 10 has sufficient tensile strength while remainingflexible.

According to one embodiment of the invention, the bend diameter of thefiber optic assembly 10 having twelve subunit fiber optic cables 100 isless than two inches (50.8 mm) and the tensile strength is at least 100lbs. According to another embodiment, the bend diameter is less than oneinch (25.4 mm), and the tensile strength is at least 200 lbs. Accordingto yet another embodiment, the bend diameter is less than 0.5 inch, andthe tensile strength is at least 300 lbs. As shown in FIG. 5, the fiberoptic assembly 10 can be folded back on itself.

According to one embodiment of the invention, the tensile limit forallowable strain on the optical fibers in the fiber optic assembly 10having twelve subunit fiber optic cables 100 is at least 200 lbs., withthe tensile limit for each subunit fiber optic cable 100 being at least30 lbs. According to another embodiment of the invention, the tensilelimit for the fiber optic assembly 10 is at least 300 lbs., with eachsubunit fiber optic cable 100 having a tensile limit of at least 40 lbs.According to another embodiment of the invention, the tensile limit forthe fiber optic assembly 10 is in the range of 300 lbs to 600 lbs, witheach subunit fiber optic cable 100 having a tensile limit of at least 50lbs.

Example 1

A fiber optic assembly 10 as illustrated in FIGS. 1-2 is formed fromtwelve flame retardant fiber optic subunit cables 100. The subunitcables 100 are single fiber cables SZ stranded together. The fiber opticassembly 10 has a minimum bend such that it can be folded back on itself(FIG. 5) and a tensile strength of at least 300 lbs. A pair of outerbinders 110, 114 made from polyester are contra-helically stranded aboutthe outer layer 130 of nine subunit cables 100. An inner binder 118 ishelically wound about an inner layer 120 of three inner subunit cables100. Each subunit cable 100 has a diameter of 2.9 mm. The cable diameterCD is 11.1 mm. The fiber optic assembly 10 has no outer jacket orcentral strength member. The tensile rating for each subunit fiber opticcable is 50 lbs. The fiber proof stress of the inner three subunitcables 100 is 200 kpsi, and the fiber proof stress for the outer ninesubunit cables 100 is 100 kpsi. The higher fiber proof stresses for theinner subunit cables 100 accommodates the higher level of axial strainof the inner subunit cables as compared with the outer subunit cables100.

One relevant test limit for tensile performance requires the short termfiber strain to be less than 60% of the fiber proof test. Varying theproof test between the inner and outer layers ensures that all twelvefibers will reach their 60% proof test limit at approximately the sametime resulting in a high tensile strength rating in the range of 300 to600 lbs.

According to the above-described embodiments, the low bend diameter andsmall cross-sectional area in part allow the fiber optic assembly 10 tobe bent around corners and otherwise introduced into tight spaces orthrough apertures, while maintaining acceptable attenuation lossperformance. The fiber optic assembly 10 is therefore particularlysuited for providing fiber optic service indoors to structures such asmultiple dwelling units (MDU). In one method of installation, the fiberoptic assembly 10 could be placed in a corner molding raceway and singlefiber subunit cables 100 can be dropped at each apartment of a MDU.While the subunit cables 100 can be stranded in various ways, SZstranding provides ease of access at midspan locations of the assembly10.

FIG. 8 is a perspective view of a portion of a fiber optic assembly 200or bundled optical cable according to a second embodiment of theinvention. FIG. 9 is a cross-sectional view of the fiber optic assembly200 taken on line 9-9 in FIG. 8. The arrangement of the assembly 200 canbe generally similar to the cable 10 shown in FIGS. 1 and 2. As in thecable 10, the fiber optic assembly 200 comprises an inner layer 320 ofthree subunit fiber optic cables 300 surrounded by an outer layer 330 ofnine cables 300. A pair of oppositely helically wound outer or externalbinders 310, 314 are wound about the external periphery of the bundle ofsubunit cables 300. The assembly 200 does not, however, include an innerbinder around the inner layer 320.

In the illustrated embodiment, the subunit cables 300 are SZ strandedtogether, with a reversal point generally indicated at 334. The outerbinders 310, 314 may be contra-helically stranded about the outer layer330 of subunit cables 300. In general, the lay length of the helicallywrapped external binders 310, 314 is smaller than the lay length of thesubunit cables 300, but other suitable lay lengths are possible. Theadjoining inner and outer layers 320, 330 of subunit cables 300 can bestranded in separate passes on separate stranders or on a commonstrander in a single pass. The binders 310, 314 can be made from, forexample, high strength materials formed from tensile yarns, such asaramid, fiberglass, polyester and other tensile yarns. The subunit fiberoptic cables 300 used in the fiber optic assembly 200 can be similar tothe subunit cables 100 shown in FIG. 1. The subunit cables 200, however,may have a smaller outside diameter, such as, for example, 2.0 mm, or1.65 MM.

The subunit fiber optic cables 200 can be, for example, flame retardantsingle fiber cables. In the illustrated embodiment, the subunit fiberoptic cables 300 include a single optical fiber 350 surrounded by abuffer coating 354 applied over the optical fiber 350. The optical fiber350 may contain a core and a cladding surrounding the core, with one ormore polymer coatings applied over the cladding. A layer 358 of loosetensile strength members surrounds the buffer coating 354, and an outerpolymer tubular subunit jacket or sheath 360 is extruded over the layer358 of strength members. The buffer coating 354 and layer 358 may beformed of materials as discussed above regarding the buffer coating 154and layer 158, respectively. The optical fibers 350 used in the subunitfiber optic cables 300 may be bend-insensitive optical fibers such asthe ClearCurve™ brand of optical fibers available from CorningIncorporated. The subunit cables 200 of the inner layer 320 may beimmediately adjacent and contacting those of the outer layer 330, withno element being interposed between the layers.

The fiber optic assembly 200 having twelve subunit fiber optic cables300 may have a cable diameter CD, approximated as discussed above forthe cable 10, of about 10 mm or less. In another embodiment, the cablediameter CD may be about 8 mm or less. Small assembly diameter ensuresthat the fiber optic assembly 200 can be routed through a short sectionof ½ inch (12.7 mm) conduit. As in the case of the cable 10, no outsidecable sheath or central strength member is required, which in partprovides the fiber optic assembly 200 with its relatively low benddiameter D. The layers 358 provide tensile strength to each subunit 300of at least 120 Newtons maximum short-term tensile load. According toone embodiment, for a subunit outside diameter of 1.65 mm, maximumshort-term tensile load is at least 150 Newtons.

Example 2

A fiber optic assembly 200 as illustrated in FIGS. 8 and 9 is formedfrom twelve flame retardant fiber optic subunit cables 300. The subunitcables 300 are single fiber cables SZ stranded together and havingClearCurve™ single mode bend insensitive fibers. A pair of outer binders310, 314 made from polyester are contra-helically stranded about theouter layer 330 of nine subunit cables 300. Each subunit cable 300 hasan outside diameter of 1.65 mm. The average cable diameter CD is about 6mm. The fiber optic assembly 200 has no outer jacket or central strengthmember. The maximum short-term tensile load for each subunit fiber opticcable 300 is 150 Newtons.

FIG. 10 is a perspective view of a portion of a fiber optic assembly 600or bundled optical cable according to a third embodiment of theinvention. FIG. 11 is a cross-sectional view of the fiber optic assembly600 taken on line 11-11 in FIG. 10. The fiber optic assembly 600comprises an inner layer 620 of one subunit fiber optic cable 300surrounded by an outer layer 630 of five cables 300. A pair ofoppositely helically wound outer or external binders 610, 614 are woundabout the external periphery of the bundle of subunit cables 600. In theillustrated embodiment, the subunit cables 300 are SZ stranded together,with a reversal point generally indicated at 634. The outer binders 610,614 may be contra-helically stranded about the outer layer 630 ofsubunit cables 300. In general, the lay length of the helically wrappedexternal binders 610, 614 is smaller than the lay length of the subunitcables 300. The exemplary 1.65 mm outside diameter subunit cables 300are suitable for use in any of the embodiments described in thisspecification.

The fiber optic assembly 600 having six subunit fiber optic cables 300may have a cable diameter CD, approximated as discussed above for thecable 10, of about 6.5 mm or less. In another embodiment, the cablediameter CD may be about 5.5 mm or less. Keeping the size low ensuresthat the fiber optic assembly 600 can be easily routed through a shortsection of ½ inch (12.7 mm) conduit.

The fiber optic assembly 600 can have a very small bend diameter whilemaintaining acceptable attenuation losses. FIG. 12 is a plot of deltaattenuation for fibers in selected subunit cables 300 when subjected toa mandrel wrap test at a wavelength of 1550 nm. The mandrel sizes were10 mm and 15 mm. FIG. 13 is a plot of delta attenuation for fibers inselected subunit cables 300 when subjected to a corner bend test undervarious loads at a wavelength of 1550 nm.

Example 3

A fiber optic assembly 600 as illustrated in FIGS. 10 and 11 is formedfrom six flame retardant fiber optic subunit cables 300. The subunitcables 300 are single fiber cables SZ stranded together and havingClearCurve™ single mode bend insensitive fibers. A pair of outer binders610, 614 made from polyester are contra-helically stranded about theouter layer 630 of nine subunit cables 300. Each subunit cable 300 has adiameter of 1.65 mm. The cable diameter CD is 4.8 mm. The fiber opticassembly 600 has no outer jacket or central strength member. The maximumshort-term tensile load for each subunit fiber optic cable 300 is 150Newtons.

Table 1 describes attenuation data for the cable assembly 600 of FIG.10, using ClearCurve™ single mode fiber in the subunit cables 300, in amandrel wrap test using a 15 mm diameter mandrel with varying numbers ofwraps, at a wavelength of 1550 nanometers.

TABLE 1 15 mm Mandrel Wrap Delta Attenuation at 1550 nanometers ColorWrap # delta attenuation (dB) Aqua 1 0.00 Aqua 2 0.02 Aqua 3 0.05 Aqua 40.08 Aqua 5 0.10 Rose 1 0.01 Rose 2 0.02 Rose 3 0.04 Rose 4 0.03 Rose 50.05 Red 1 0.03 Red 2 0.07 Red 3 0.08 Red 4 0.11 Red 5 0.12

As shown in Table 1, each of the three tested fibers in the subunits ofthe cable assembly 600 experience an absolute delta attenuation value ofless than 0.2 dB at 1550 nm under up to five wraps about the 15 mmmandrel. Each of the three tested fibers experience a delta attenuationof less than 0.2 dB under up to three wraps about the 15 mm mandrel.Each of the three tested fibers experience a delta attenuation of lessthan 0.15 dB under up to four wraps about the 15 mm mandrel. Each of thethree tested fibers experience a delta attenuation of less than 0.10 dBunder up to two wraps about the 15 mm mandrel. Each of the three testedfibers experience a delta attenuation of less than 0.05 dB under up toone wrap about the 15 mm mandrel.

Table 2 describe attenuation data for cable assembly 600 if FIG. 11using ClearCurve™ single mode bend insensitive fiber in the subunitcables 300, in a mandrel wrap test using a 10 mm diameter mandrel, undervarying numbers of wraps, at a wavelength of 1550 nanometers.

TABLE 2 10 mm Mandrel Wrap Delta Attenuation at 1550 nanometers ColorWrap # delta attenuation (dB) Aqua 1 0.04 Aqua 2 0.13 Aqua 3 0.17 Aqua 40.21 Aqua 5 0.29 Rose 1 0.02 Rose 2 0.08 Rose 3 0.10 Rose 4 0.15 Rose 50.16 Red 1 0.07 Red 2 0.12 Red 3 0.23 Red 4 0.28 Red 5 0.36

As shown in Table 2, each of the three tested fibers of the cableassembly 600 experience an absolute delta attenuation value of less than0.5 db at 1550 nm under up to five wraps about the 10 mm diametermandrel. Each of the three tested fibers experience an absolute deltaattenuation value of less than 0.4 db at 1550 nm under up to three wrapsabout the 10 mm diameter mandrel. Each of the three tested fibersexperience an absolute delta attenuation value of less than 0.3 db at1550 nm under up to four wraps about the 10 mm diameter mandrel. Each ofthe three tested fibers experience an absolute delta attenuation valueof less than 0.2 db at 1550 nm under up to two wraps about the 10 mmmandrel. Each of the three tested fibers experience an absolute deltaattenuation value of less than 0.1 db at 1550 nm under up to one wrapabout the 10 mm mandrel.

Table 3 describe attenuation data for cable assembly 600 if FIG. 11using ClearCurve™ single mode fiber in the subunit cables 300, in acorner bend test under various loads, at 1550 nanometers.

TABLE 3 Corner Bend Delta Attenuation at 1550 nanometers Color Wgt. (kg)delta attenuation (dB) Aqua 2 0.01 Aqua 6 0.06 Aqua 10 0.14 Aqua 14 0.25Rose 2 0.03 Rose 6 0.14 Rose 10 0.56 Rose 14 0.61 Yellow 2 0.04 Yellow 60.18 Yellow 10 0.21 Yellow 14 0.18

As shown in Table 3, each of the three tested fibers of the cableassembly 600 experiences an absolute delta attenuation value of lessthan 0.6 dB under a load of 10 kilograms at 1550 nm in the corner bendtest. Each of the three tested fibers experiences a delta attenuationvalue of less than 0.3 under a load of 6 kilograms in the corner bendtest. Each of the three tested fibers experiences a delta attenuationvalue of less than 0.1 under a load of two kilograms in the corner bendtest.

According to one aspect of the present invention, the subunit cables ofthe fiber optic assemblies can be colored according to industry standardcode. The fiber optic assemblies could be placed in a corner moldingraceway and single fiber subunit cables can be dropped at each apartmentof a MDU. Each individual cable can also have a unique print identifierto facilitate connection to the correct FDT port. For example, at afirst living unit of an MDU, the technician can access the subunit cable300 with “CONN 1” printed thereon. The second living unit can receivethe white subunit cable 300 with “CONN 2” printed thereon, and so onthrough the sixth subunit labeled “CONN 6.” The direction of the printcan be used to facilitate error-free installation, and can be arrangedto as to always point away from (or toward) the FDT. This enables thetechnician to cut the subunit cable and reliably drop to the properlocation. This is an important feature because the technician musttypically cut the subunit cable at a point at least six feet past thepoint where the terminated drop is to be placed. SZ stranding providesease of access to subunit cables at midspan locations of the fiber opticassemblies. Dual six fiber color coding (e.g. blue through white andblack through aqua) can be used in twelve-fiber embodiments to providetwo paths exiting the connection closet in MDUs. The lower color fibers(e.g. blue through white), for example, can be routed to lower numberedapartments in one direction and higher color fibers (e.g. black throughaqua) can be routed in the opposite direction. Splitting groups of sixfibers in this manner reduces the amount of cable needed per floor.

According to the above-described embodiments, the low bend diameter andsmall cross-sectional area in part allow the fiber optic assemblies tobe bent around corners and otherwise introduced into tight spaces orthrough apertures, while maintaining acceptable attenuation lossperformance. The fiber optic assemblies are therefore particularlysuited for providing fiber optic service indoors to structures such asmultiple dwelling units (MDU).

The illustrated embodiments show fiber optic cable assemblies having aplurality of single fiber subunit cables. Subunit fiber optic cableshaving more than one optical fiber, such as two, three or more opticalfibers, may also be used in fiber optic cable assembly embodimentsconstructed according to the principles of the present invention.Further, varying numbers of subunit cables, such as eight, twenty-four,etc., can be arranged into a fiber optic cable assembly according to thepresent invention.

Many modifications and other embodiments within the scope of the claimswill be apparent to those skilled in the art. For instance, the conceptsof the present invention can be used with any suitable fiber optic cabledesign and/or method of manufacture. For instance, the embodiments showncan include other suitable cable components such as an armor layer,coupling elements, different cross-sectional shapes, or the like. Thus,it is intended that this invention covers these modifications andembodiments as well those also apparent to those skilled in the art.

1. A fiber optic assembly, comprising: a plurality of SZ strandedsubunit fiber optic cables, each subunit fiber optic cable comprising:at least one optical fiber; a layer of loose tensile strength memberssurrounding the at least one optical fiber; and a subunit jacketsurrounding the layer of loose tensile strength members; and at leastone binder wound around an outer periphery of the plurality of subunitfiber optic cables.
 2. The fiber optic assembly of claim 1, wherein theplurality of subunit fiber optic cables comprises twelve subunit fiberoptic cables and an average diameter of the fiber optic assembly is lessthan 12.5 mm.
 3. The fiber optic assembly of claim 2, wherein theplurality of subunit fiber optic cables is arranged as an inner layer ofthree subunit fiber optic cables and an outer layer of nine subunitfiber optic cables surrounding the inner layer.
 4. The fiber opticassembly of claim 3, wherein the average diameter of the fiber opticassembly is less than 11.5 mm.
 5. The fiber optic assembly of claim 3,wherein the average diameter of the fiber optic assembly is less than8.0 mm.
 6. The fiber optic assembly of claim 5, wherein a diameter ofthe subunit cables is about 1.65 mm.
 7. The fiber optic assembly ofclaim 1, wherein the plurality of subunit fiber optic cables comprisessix subunit fiber optic cables and an average diameter of the fiberoptic assembly is less than 10.0 mm.
 8. The fiber optic assembly ofclaim 7, wherein the plurality of subunit fiber optic cables is arrangedas an inner layer of one subunit fiber optic cable and an outer layer offive subunit fiber optic cables surrounding the inner layer.
 9. Thefiber optic assembly of claim 8, wherein the average diameter of thefiber optic assembly is less than 6.5 mm.
 10. The fiber optic assemblyof claim 8, wherein the average diameter of the fiber optic assembly isless than 5.5 mm.
 11. The fiber optic assembly of claim 8, wherein adiameter of the subunit cables is about 1.65 mm.
 12. The fiber opticassembly of claim 8, wherein at least one of the subunit cablesexperiences a delta attenuation of less than 0.5 dB at 1550 nm whenwrapped five times about a 10 mm mandrel.
 13. The fiber optic assemblyof claim 8, wherein at least one of the subunit cables experiences adelta attenuation of less than 0.6 dB under a load of 10 kilograms at1550 nm in a corner bend test.
 14. The fiber optic assembly of claim 1,wherein the at least one binder comprises two binders contra-helicallywound about the outer periphery of the plurality of subunit fiber opticcables.
 15. The fiber optic assembly of claim 1, wherein the subunitjackets comprise PVC.
 16. The fiber optic assembly of claim 1, whereinthe tensile strength members comprise aramid yarn, the at least onebinder is free of an outer jacket, and the assembly is free of a GRPstrength member.
 17. The fiber optic assembly of claim 1, wherein a benddiameter of the fiber optic assembly is less than one-half inch (12.7mm).
 18. The fiber optic assembly of claim 1, wherein a tensile strengthof the subunit fiber optic cables is at least 40 lbs.
 19. A fiber opticassembly, comprising: at least six subunit fiber optic cables, eachsubunit fiber optic cable comprising: at least one optical fiber; alayer of loose aramid tensile strength members surrounding the at leastone optical fiber; and a PVC subunit jacket surrounding and contactingthe layer of loose aramid tensile strength members; and at least twobinders contra-helically around an outer periphery of the plurality ofsubunit fiber optic cables, wherein the binders are free of an outerjacket, and an average diameter of the fiber optic assembly is less than12.5 mm.
 20. A fiber optic assembly, consisting essentially of: six SZstranded subunit fiber optic cables, each subunit fiber optic cablecomprising: at least one optical fiber; a tight buffer layer surroundingthe at least one optical fiber; a layer of loose tensile strengthmembers surrounding the tight buffer layer; and a subunit jacketsurrounding the layer of loose tensile strength members; and at leastone outer binder wound around an outer periphery of the plurality ofsubunit fiber optic cables, wherein an average diameter of the fiberoptic assembly is 12.5 mm or less.